Two-Dimensional Infrared Spectroscopy of Metal Carbonyls

Abstract

Metal carbonyl complexes offer both rich chemistry and complex vibrational spectroscopy due to strong coupling among the carbonyl stretches. Using two-dimensional infrared (2DIR) spectroscopy, it is possible to resolve the underlying transitions between vibrational energy levels, determine the orientations and relative magnitude of the corresponding transition dipole moments, measure the coupling between modes due to the anharmonicity of the potential, and probe energy redistribution among the modes as well as energy relaxation to other degrees of freedom. Measurements on metal carbonyl complexes have played, and continue to play, a crucial role in facilitating the development of 2DIR spectroscopy. These compounds have provided powerful demonstrations of the unique ability of 2DIR spectroscopy to resolve vibrational structure and dynamics in multimode systems. In addition, invaluable new information has been obtained on metal-to-ligand charge transfer processes, solvent-solute interactions and fluxionality. Since transition metal complexes play important roles in catalysis and as dye sensitizers for semiconductor nanoparticle photocatalysis, detailed probes of equilibrium and phototriggered dynamics should aid our understanding of these key catalytic systems. The richness and level of detail provided by the 2DIR spectra of metal carbonyl complexes turn them into extremely useful model systems for testing the accuracy of ab initio quantum chemical calculations. Accurate modeling of the 2DIR spectra of solvated metal carbonyl complexes requires the development of new theoretical and computational tools beyond those employed in the standard analysis of one-dimensional IR spectra, and represents an ongoing challenge to currently available computational methodologies. These challenges are further compounded by the increasing interest in triggered 2DIR experiments that involve nonequilibrium vibrational dynamics on multiple electronic potential surfaces. In this Account, we review the various metal carbonyl complexes studied via 2DIR spectroscopy and outline the theoretical approaches used in order to model the spectra. The capabilities of 2DIR spectroscopy and its interplay with modern ab initio calculations are demonstrated in the context of the metal carbonyl complex Mn(2)(CO)(10) recently studied in our lab. Continued progress in experimental implementation and theoretical analysis will enable transient 2D spectroscopy to provide structurally sensitive details of complex, highly interacting nonequilibrium processes that are central to diverse chemical transformations.

Effect of ion–molecule interaction on fermi-resonance in acetonitrile studied by ultrafast vibrational spectroscopy

“…However, the effect of ions on vibrational dynamics of a given molecule has begun to be investigated recently with an advent of time-resolved vibrational spectroscopic techniques such as ultrafast infrared-Raman, infrared pump-probe (IR PP), and two-dimensional IR (2DIR) experiments [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. A vibrationally excited molecule undergoes different relaxation processes on various timescales including vibrational energy transfer to anharmonically coupled vibrational modes [23,24], vibrational energy dissipation into the solvent [25], and resonance energy transfer to nearby vibrational modes with similar vibrational energies [26][27][28][29][30].…”

Waveguide-enhanced 2D-IR spectroscopy in the gas phase

“…In particular, over the last 15 years, 2D-IR spectroscopy [1][2][3] has been successfully applied to studies of a range of structural dynamics [4,5] and energy transfer processes [6,7]. A wide range of approaches involve pulsed IR excitation and IR probing of samples providing detailed dynamical information about vibrational processes in molecules.…”

Laser-driven localization of collective CO vibrations in metal-carbonyl complexes

“…For instance, anharmonic couplings between collective normal modes can be studied in quite some detail using ultrafast two-dimensional IR spectroscopy. Taking metal-carbonyl compounds as an example, anharmonic couplings [1] and spectral diffusion [2] have been studied for Mn 2 (CO) 10 .…”